This invention relates to certain catalysts useful for preparing polyolefins, especially syndiotactic polyolefins, comprising certain Group 4 metal complexes in combination with one or more activating cocatalysts. More particularly, the metal of such complexes is covalently bonded to a cyclic group with a delocalized .pi.-system (which optionally may be substituted as explained hereinafter) and also bonded to a C.sub.4-40 conjugated or nonconjugated diene. Included are such complexes wherein the metal is in the +2 or +4 formal oxidation state. The invention further relates to addition polymerization processes using such complexes.
The preparation and characterization of certain biscyclopentadienyl zirconium and hafnium diene complexes are described in the following references: Yasuda, et al., Organometallics, 1, 388 (1982), (Yasuda I); Yasuda, et al. Acc. Chem. Res., 18, 120 (1985), (Yasuda II); Erker, et al., Adv. Organomet. Chem., 24, 1 (1985) (Erker, et al. (I)); and U.S. Pat. No. 5,198,401. The latter reference describes the use of biscyclopentadienyl zirconium diene complexes as olefin polymerization catalysts in combination with ammonium borate cocatalysts.
The preparation of certain Ti, Zr, and Hf monocyclopentadienyl diene complexes was described in Yamamoto et al., Organometallics, 8, 105 (1989) (Yamamoto) and Blenkers, J, et al., Organometallics, 6, 459 (1987) (Blenkers). Only the Hf complexes disclosed in the latter reference were described as having utility as catalyst components.
Biscyclopentadienyl titanium complexes in which the titanium is in the +4 oxidation state, and olefin polymerization catalysts formed from such by combination with an activating agent, e.g., alumoxane or ammonium borate, are well known in the art. Thus, U.S. Pat. No. 3,242,099 describes the formation of olefin polymerization catalysts by the combination of biscyclopentadienyl titanium dihalides with alumoxane. U.S. Pat. No. 5,198,401 discloses tetravalent biscyclopentadienyl titanium complexes, including at col. 9, lines 24-27 diene containing complexes and olefin polymerization catalysts obtained by converting such complexes into cationic form. Particularly preferred catalysts are obtained by the combination of ammonium borate salts with the biscyclopentadienyl titanium complexes.
Titanium and zirconium complexes, including monocyclopentadienyl complexes in which the metal is in the +4 oxidation state, are also known in the art. Examples of the foregoing references include: U.S. Pat. Nos. 5,064,918, 4,774,301, 5,045,517 and 4,808,680.
In copending application, Ser. No. 08/082,197 filed Jun. 24, 1993, there are disclosed monocyclopentadienyl complexes having a cyclic structure in which the titanium is in the +2 formal oxidation state. The application also teaches the formation of olefin polymerization catalysts from such complexes by the combination of the complex with activator compounds such as alumoxanes, borate salts and strong Lewis acids. The teachings of all of the foregoing patents, patent applications and publications are hereby incorporated by reference.
The present invention provides novel addition polymerization catalysts which can be employed over a wide range of physical conditions and with a wide range of monomers and combinations of such monomers, thus providing an outstanding opportunity of making polymers having specifically desired properties. In particular the present catalysts have been found to be particularly suited for the preparation of polymers having a high degree of syndiotacticity, most suitably, syndiotactic monovinylidene aromatic polymers have been prepared using the present catalysts.